In the field of orthodontics there has been an increasing demand for brackets that are visually aesthetic. In response to this need, various materials have been suggested for making orthodontic brackets. Various ceramic materials have been used in making orthodontic brackets. However, orthodontic brackets made from ceramic materials are quite brittle and thus are subject to fracture. Additionally, ceramic materials are substantially more expensive to produce than typical prior art metal brackets.
Plastic materials have also been suggested for use in making orthodontic brackets. However, plastic orthodontic brackets have been found to be unsatisfactory due to their inability to provide the appropriate strength necessary over the long periods of time for which the orthodontic brackets are typically used. In order to improve the strength of a plastic orthodontic bracket, it has been suggested to provide metal reinforcement such as illustrated in U.S. Pat. No. 3,930,311, issued Jan. 6, 1976 and U.S. Pat. No. 4,107,844, issued Aug. 22, 1978 and/or the use of metal inserts in the archwire slot as shown in U.S. Pat. No. 4,299,569, issued Nov. 10, 1981 and U.S. Pat. No. 4,302,532, issued Nov. 24, 1981. In the '311 patent there is disclosed an orthodontic bracket which uses a sheet metal stiffening core embedded in the plastic which extends in the direction substantially perpendicular to the longitudinal axis of the archwire slot and is designed so as to reinforce the wings projecting on either side of the bracket. The '844 patent used metal reinforcements embedded within the bracket. The '569 patent discloses a metal insert which extends along the length of the archwire slot and comprises a generally U-shaped cross-section configuration. In the '532 patent, various metal insert configurations are disclosed for placement in the archwire slot. While the metal inserts of the '569 and '532 patents provide improved strength to the archwire slot, the overall strength of the bracket is substantially limited by the plastic material of the orthodontic bracket. Over time, the plastic tends to deform due to the constant force being applied to the bracket by the orthodontic archwire. Additionally, due to the configuration of the insert, the insert can be pulled out in a direction away from the bonding base of the bracket.
It has also been suggested in the prior art to make brackets of a plastic material reinforced with a filler. However, over time, the glass filled plastic bracket tends to distort and, thus, loose their effectiveness as an orthodontic appliance.
Applicants have invented an improved plastic orthodontic bracket which minimizes or eliminates many of the problems of the prior art.